Help with RAMPS LCD

Hello again,
sorry I haven’t posted for a while - I started a long-term cover at a secondary school a few weeks ago (I don’t normally do ‘long term’ since I prefer to work a couple of days a week to supplement my teacher pension - but my agent batted her eyelids at me and I’m a sucker for a pretty face :slight_smile: ) and I have been pretty busy getting to grips with new classes and the like.
Anyhoo…The computer room which is my teaching area is bland and boring. I’ve done the usual sticking up kids work and tech posters, but there is still something missing. I came across an interesting project called PolarPlot which is essentially a vertical drawing machine, using 2 stepper motors, driven through an Arduino RAMPS setup to make a basic plotter (diagram below). Since I now have a little experience with 3D printers I thought that this was something I could tackle and, better yet, build it on a bare wall in my room. When the kids get bored of me prattling on, they will be able to watch the plotter drawing on the wall :slight_smile:
So, I’ve built the basic machine, using bathplug chain, a couple of Nemo 17s and a few odds and sods, and it is now time to put the controller in place. I had a spare Arduino 2560, so I ordered a RAMPS 1.4 shield, a few A4988 stepper drivers and a cheap LCD display screen. I uploaded the code to the Arduino/Ramps with no issues BUT now comes the problem. When I hook the LCD screen up to the RAMPS board the screen lights up but nothing is displayed. I thought that it might be the code, so I uploaded a copy of Marlin customised for this exact LCD screen (a 12864 clone), but the result was the same.
I trawled the web for solutions and came across a suggestion that the ribbon cable sockets (2 x 10pin sockets in a 2x5 arrangement) are sometimes the wrong way around on some cheaper clones. I filed the key off the ends of the ribbon cables so I could reverse them, but then there was no output at all - not even backlight. Next I tried swapping the ribbon cables and discovered that the screen lights-up if one of the cables connects one of the ports to the RAMPS adaptor, but if I try the other, apparently identical ribbon then it remains dark. Assuming that both cables are required, my best guess is that I have a dodgy ribbon cable. Before I resort to breaking-out the multimeter and testing each ribbon I thought it would be worth posting here to see if anyone has expertise in this area, or has come across a similar problem. It also gave me an excuse to post and keep in touch with the people who have been so welcoming and helpful on these forums.

Any suggestions?

Diagram of the PolarPlot device

Picture of the RAMPS/LCD kit

That style of connector doesn’t often have a bad connection in my experience, and testing with multimeter would be only way to find it… But if one cable acts different from the other, chances seem pretty high that you got a bad cable!

Yes, I feel you are right and I also find it odd - I’ve never come across a dodgy ribbon cable that had no physical sign of damage, and I’ve used plenty over the years…

Looks like you were right. I just ran a quick continuity test on pin 1, and one ribbon is fine but the other is open circuit. Bugger. My first thought was that they could be wired differently, but the red stripe has always been pin1 to me, and I can’t imagine they would wire the connectors differently.

I just put the cable under my scope and blow-me, it is trashed at one end - Damn Chinese QC. :slight_smile: